It is generally known in antifriction bearing technology that needle bushes are the design of needle bearings which have the smallest radial overall height and make bearings possible which are particularly space-saving and simple to assemble with a high radial load-bearing capability. They are used in virtually all areas of the technology and comprise substantially a thin-walled outer ring which can be inserted into a housing hole and has two radially inwardly directed rims on its axial sides, and a needle ring which is held in the outer ring by said rims and is formed by a needle cage and a multiplicity of bearing needles which are guided in the latter at uniform spacings in the circumferential direction. Here, the bearing needles roll on the inner circumferential face of the outer ring, which inner circumferential face is configured as a raceway, and on the outer circumferential face of the shaft to be mounted, which outer circumferential face is likewise configured as a raceway, or, if the shaft cannot be configured as a raceway, on the outer circumferential face of a separate inner ring. Moreover, in the case of sealed needle bush embodiments, at least two seals are arranged axially next to the side faces of the needle cage within the needle bush, which seals are known in a multiplicity of various embodiments and protect the needle bush against contaminants from the outside and the loss of lubricant.
It is known, for example, from DE 42 35 117 A1 and DE 10 2006 053 716 A1 to seal a needle bush by way of two lip seals which are arranged on both sides next to the needle cage, are of C-shaped profile cross section, and one profile limb of which bears against that part of the inner circumferential face of the outer ring which is arranged between the respective rim and the needle cage, whereas the other profile limb of which, which points in each case toward the rims of the outer ring, rests rubbingly on the circumferential face of the shaft which is to be mounted.
Furthermore, it is known from DE 1 888 002 U1 to use two rubber seals which have a horizontal Z-profile in cross section as seals for a needle bush, which rubber seals seal with their free ends of one radial profile limb in each case the angled regions between the inner circumferential face of the outer ring and the rims and rest rubbingly with their other ends on the circumferential face of the shaft which is to be mounted. The adjoining profile web of said seals then extends obliquely upward into the interior of the needle bush, in each case as far as below the needle cage, and the adjoining second radial profile limb likewise rests rubbingly with its free end on the circumferential face of the shaft which is to be mounted.
Moreover, it is also known from DE 6 908 931 U1 and DE 7 035 926 U1 to arrange a seal on the end face of a radial rim of a needle bush. In DE 6 908 931 U1, said seal is configured here as a rubber sealing ring which is vulcanized on and has a shoulder which bears against the end face of the rim and a collar which protrudes into the needle bush and on which a sealing lip is formed integrally which rests rubbingly on the circumferential face of the shaft which is to be mounted. In DE 7 035 926 U1, in contrast, the seal is formed by a separate rubber lip seal which, on its upper side, has a circumferential annular groove for plugging the seal onto the rim end face and, on its underside, has one or more sealing lips which rests/rest rubbingly on the circumferential face of the shaft which is to be mounted.
Furthermore, it is known from DE 2 221 234 A1, in order to seal a needle bush, to insert two sealing rings which have a horizontal U-profile in cross section into the outer ring in such a way that they bear with their uppermost axial profile limb and their radial profile web against the inner circumferential face of the outer ring and against the inner circumferential face of the rims. The second profile limb of said sealing rings which adjoins the profile web is configured as a sealing lip arm which protrudes into the needle bush, at the end of which sealing lip arm a sealing lip is integrally formed which is shaped as a V-profile and into which a tension spring or a resilient ring which braces the sealing lip against the shaft which is to be mounted is inserted.
Finally, it is also known from DE 1 575 697 A1 to seal a needle bush by way of seals which are arranged on the outer circumferential face of the rims of the outer ring. To this end, the rims in each case have an axially inwardly directed right-angled bend with a circumferential sealing ring which is vulcanized on, has various straight or angular profile cross sections and is configured with one or more sealing lips which is/are in sealing contact rubbingly with the shaft which is to be mounted. In the embodiments with angular profile cross sections, moreover, the sealing ring extends along the end face of the rims as far as into the interior of the needle bush and has a single sealing lip at the end of one or the other profile limb.
All the above-described solutions have the common disadvantage, however, that the seals which are used do not have a sufficient sealing action, in order for it to be possible to use them as needle bushes which are configured as a throttle valve bearing for pivotably mounting the throttle valve shaft of a regulating device for exhaust gas recirculation in internal combustion engines. The reason for this is that throttle valve bearings of this type in exhaust gas recirculation regulating devices are subjected to correspondingly increased amounts of exhaust gas condensates as the amounts of what are known as blow-by gases increase, which exhaust gas condensates penetrate via the housing holes for the throttle valve shaft to the throttle valve bearings. Said exhaust gas condensates have a composition which is from oily/watery to watery/acidic, with the result that the needle bushes which as a rule are composed of a hardened roller bearing steel are subjected first of all to intensified attack from external corrosion which continues as far as into the interior of the needle bushes even in the case of multiple sealing of said needle bushes by way of known seals. Here, the condensate first of all forms a rust layer on the outer circumferential face of the rim of the needle bushes, which rust layer, during further advancing of the corrosion, spreads out over the end faces of the rims by way of rust infiltration of the seals as far as into the interior of the needle bushes, with the result that damage and the failure of the throttle valve bearings associated with the functional failure of the throttle valve occur.